Process for separating non-metallic inclusions from hot liquid metal

ABSTRACT

The disclosure relates to a process for separating non-metallic inclusions from hot liquid metal, in particular from aluminum killed soft steel, in continuous casting plants, wherein the metal supplied into a tundish is guided at least once in upward direction to the surface of the metal sump in said tundish under formation of at least one stream at a speed greater than that of the metal in the tundish prior to its being deflected, whereby a wave is formed at the surface of the metal covered by slag. The metal is guided towards the surface of the metal sump by means of a partition wall having at least one opening from which a canal extends in upward direction to end at a distance of from 3 to 30 cm below the metal sump surface.

United States Patent 1191 Listhuber et al. June 4, 1974 [54] PROCESS FOR SEPARATING 3,094,424 6/1963 Ratcliffe, l64/28l ux NON-METALLIC INCLUSIONS FROM nor g l LIQUID METAL pelt et a [75] Inventors: Friedrich Listhuber; Thorwald Fastner; Ernst Bachner, all of Linz, Pnmw'y Exammer R Spencer Annear Austria Attorney, Agent, or F1rmBrumbaugh, Graves. Donohue 8L Raymond [73] Ass1gnee: Vereinigte Osterreichische Eisenund Stahlwerke Alpine Montan Aktiengesellschaft, Linz, Austria [57] ABSTRACT 'I 72 [22] F1 ed June 1 19 The disclosure relates to a process for separatlng non- Appl- 258,671 metallic inclusions from'hot liquid metal, in particular from aluminum killed soft steel, in continuous casting 0 plants, wherein the metal supplied into a tundish is [3 1 Foreign App lc at lon y- Data guided at least once in upward d1rection to the surface June 4, 1971 Austria the metal p in said tundish under formation of Nov. l4, l97l Austrla 9483/7l at least one stream at a Speed greater than that of the metal in the tundish prior to its being deflected, g 'i 164/82 5 whereby'a wave is formed at the surface of the metal l 134 281. covered by slag. The metal is guided towards the sur- 1 earc l 1 face of the metal sump by means of a partition wall having at least one opening from which a canal ex- 56 f d tends in upward direction to end at a distance of from Re erences 3 to 30 cm below the metal sump surface.

UNITED STATES PATENTS 214.746 4/1879 Baker l64/l34 x 4 Claims, 11 Drawing Figures PATENTEDJun- 4 .914 2 sum 2 or 4' U FIG;4

PROCESS FOR SEPARATING NON-METALLIC INCLUSIONS FROM HOT LIQUID METAL The invention relates to a process for separating nonmetallic inclusions from hot liquid metal, in particular from aluminum killed softsteel, in a continuous casting plant, in which the metal is supplied into a tundish and after formation of a metal sump covered by a slag layer permitted to flow out of said tundish through at least one draining tube into a water-cooled mould from which the solidifying cast bar is continuously drawn out; and to a tundish for carrying out such process.

It is known that non'metallic inclusions decrease the shapeability of metals, lead to surface flaws in the rolled product and impair the mechanical properties of the end product. Thus, e.g. in soft, aluminum killed steel which is processed to cold rolled sheets for use in car manufacture as autobody sheets, it is necessary to keep the content of non-metallic inclusions as low as possible, because otherwise the high demandsplaced in the shapeability and surface quality of these sheets cannot be met. Non-metallic inclusions in aluminum killed steels as a rule are aluminum oxides which are created while the steel is deoxidized. The aluminium may also oxidize to the formation of aluminum oxides when the aluminumcontaining steel gets into contact with air, e.g. when the steel stream runs into a casting form or into a tundish arranged in front of such form. Although these non-metallic inclusions have a specific weight considerably below that of the liquid steel, these inclusions do not separate by themselves by floating up when the steel rests in the casting ladle or in the-tundish, respectively; rather, a considerable amount of small particles remains suspended in the steel which impairs the quality of the cold rolled sheets produced out of such steel. 1

In order to avoid these difficulties a process has been described in the German provisional publication No. 1,959,570 in which it is proposed to use, in continuous casting, casting tubes with closed bottoms and lateral. outflow openings from which the steel runs out and upwardly below the steel level in the continuous casting mould so that the non-metallic inclusions which deposit at the already solidified bar shell are flushed off and guided to the surface. By this processit becomes possible to reduce the content of non-metallic inclusions in the marginal zone of "the steel bar, but the overall content of non-metallic inclusions remains-relatively high because in a continuous casting mould the conditions for cleaning the steel by separating non-metallic particles are unfavourable. in particular when wide slabs are produced in which the ratio between width and thickness is great; the cross section of a continuous casting mould'is relatively small so that the metal level is not sufficiently great for a complete separation of the nonmetallic inclusions. Also, it is possible that in this process turbulences occur in the current which sometimes may cause non-metallic particles that were already led to the surface to be dragged into the steel again and to stay in the solidifying bar. A further disadvantage resides in that for adapting the current to different cross sections (forms) of the continuous casting mould, different casting tubes have to be used. Further, the bottom of the casting tube may easily break off so that casting has to be continued with the casting stream falling down in vertical direction so that the non-metallic inclusions will penetrate deeply into the interior of the expensive.

bar. In such a case of disturbance the casting speed has to be lowered down immediately.

According to a process described in the Austrian patent No. 283,619 it has been proposed, in order to reduce the content of gas and inclusions in continuous casting, to provide the floor of the tundish, arranged between-the casting ladle and the continuous casting mould, with gas permeable flush stones, through which an inert gas, e.g. argon, is blown from below through the hot liquid metal so that oxides and sulfides suspended therein may be flushed out. Such flushing with inert gas which is also applied in casting ladies is quite effective but the flushing stones are liable to be obstructed by the metal. The flushing gas cools off the hot liquid metal to an undesired degree and also it is rather The invention is aimed at avoiding the described difficulties and disadvantages and in a process of the kind defined in the introduction resides in that the total metal when flowing through the tundish is directed at least once in upward direction to the surface of the metal sump under formation of at least one stream of a speed greater than that of the metal in the tundish prior to the deflection, whereby a wave or bulging is formed at the surface of the metal or slag, respectively; The invention utilizes for the separation in a singular manner the fact that the non-metallic particles compared to the liquid steel have a smallerwettability and specific weight. The current of the metal directed from below in upward direction is to lead each metal particle and each slag particle to the surface once, whereby the non-metallic inclusions are absorbed by the slag layer.

rected towards the surface of the metal sump or towards the slag at an angle of 30 to Further, the metal stream is to flow upwardly from 3 to 30 cm below the metal sump surface, its speed being adjusted to increase proportionally in a range of at least 3.5 to 31 cm/sec to maximally 17.5 to 45 cm/sec.

The tundish for carrying out the process according to the invention comprises at least one partition wall between inflowing and outflowing metal made of refractory material with at least one opening close to the floor, and is characterized in that behind the partition wall at least one canal of refractorymaterial directed upwardly is'provided, which opens at a distance below the metal sump surface in the tundish. The cross section of the canal in which the metal flows upwardly is smaller than the cross section area of the metal which flows in horizontal direction through the supply part of the tundish, i.e. through that part of the tundish which lies in front of the separating wall.

The cross section of the canal in the tundish is suitably so dimensioned that for a certain casting output the chosen metal stream speed is obtained.

The canal cross section may be calculated from the relation casting output is equal to the product of canal cross section and desired metal stream speed."

During casting a higher bath level is adjusted to in the tundish in the area in front of the separating wall than in the area behind it.

. 3 Suitably the distance betweenthe metal sump surface and the upper margin of the canal directed in upward direction amounts to from 3 to 30 cm.

An advantageous embodiment of the tundish resides in that a hollow body of refractory material, preferably a tubular hollow body which is open on both sides, is arranged on the floor of the tundish, the throughflow opening(s) being provided in the lower portion of said hollow body, which lower portion, at least in part, is surrounded by a structural element containing -the canal or the canals.

Owing to the tubularshape of the partition walls between the inflowing and the outflowing metal the steel yields are improved; furthermore, no long heating times are necessary and the lateral walls of the-tundish are protected because the steel is guided into the interior of the hollow body. A tundish according to the invention thus has a longer life.

According to a preferred embodiment the hollow body and the pedestal-shaped structural element surrounding the lower portion of the hollow body are made of one piece.

Suitably the tubular hollow body may be pressed onto the floor of the tundish'and fixed in position by means of a cover that may be set onto the tundish, the cover having an opening for the supply of liquid metal.

Tundishes with partition walls for dividing the tundishes into several chambers or for changing the flowing direction ofthe metal are already known per se. According to a proposal described in the Handbuch des StranggicBens by E. Herrmann. Aluminium-Verlag GmbH, Dusseldorf, 1958, page 667, an interposed trough made of refractory bricks is used for supplying molten steel to .the continuous casting mould; this trough is provided with two communicatingly connected spacesfrom which the steel flows through a notch in a partition wall into a third space in which the outflow for draining the steel into the mould is provided. This interposed trough affords a precise regulation of the metal supply into the mould because a small change in the height of the metal level in the two communicating spaces leads to great changes of the metal amount running into the third space via the notch. For casting aluminum containing steels the use of such tundishes would not be suitable, however, because when the metal enters the last space an oxidation by air would take place. Further, it has been proposed according to the German provisional publication No. 1,9l7,367 to provide in the tundish of a continuous casting plant for the addition of aluminum, aluminummagnesium-alloys, lead sulfide, iron sulfide, tellurium,

selenium and chemical compounds with tellurium and selenium to steel a wall (partition wall) transverse to the flowing direction, in order to prevent the added metals, in particular the heavy metals, from migrating directly from the inflow area at oneend of the tundish to the outflow opening at the other end, without uniformly mixing with the steel. When such a wall is used the steel has'to move upwardly from below and by that movement a complete solution or a uniform distribution of the added substances in the steel is achieved.

These substances are either to dissolve or'to form a suspension with the liquid steel and this suspension must not be broken'while the steel migrates through" the tundish.

A preferred use of tundishes according to the invention is the separation of non-metallic inclusions, in particular of aluminum oxide, from steels composed of 0 to 0.20 percent C, 0.25 to 1.60 percent Mn, 0.02. to 0.1 percent Al and if desired up to 0.30 percent Si, remainder iron and customary impurities, in particular from soft steels for cold rolled deep drawing sheets, in continuous casting. In particular it is possible to separate nonmetallic inclusions from the following metals by employing the invention. 1

Reference Data The total content of inclusions in slabs cast continuously from these steels is'extraordinarily low when the process and the device according to the invention are used and practically no flaws occur which deteriorate the surface quality of sheets produced therefrom.

In order that the invention may be more fully understood it shall now be explained with reference to the accompanying drawings. FIG. 1 shows a schematical vertical sectional view of a casting ladle, a tundish and the upper part of a continuous casting plant. F 10.2 is a vertical sectional view along line 11-11 of FIG. 1, likewise schematical. FIG. 3 is a similar representation as FIG. 1 and shows the left part of a tundish according to another embodiment of the invention. FIG. 4 is a diagram illustrating the connection between the flowing speed v in cm/sec. of the metal stream and the distance a in cm between the metal sump surface in the tundish and the-upper margin of the canal which is directed upwardly according to the invention.

FIG. 5 shows a schematical vertical sectional view of a casting ladle, a modified tundish and the upper part of a Continuous casting plant, the section being made alongthe line VV of FIG. 6. FIG. 6 is a horizontal sectional view of the left part of the tundish along the line. VI-VI of FIG. 5. FIG. 7 shows another embodimcnt for the tubular hollow body with a shoulder containing the refractory canal, in a longitudinal sectional other, as it is used for a tundish according to FIG. 9.

FIG. 11 is a top view of the tubular body according to FIG. 10. I

In FIG. 1 numeral 1 denotes the lower part of a casting ladle, from which the steel or another hot liquid metal runs as a stream 2 into a tundish 3..ln the left part of the tundish numeral 4 denotes a partition wall made of refractory material which divides the tundish into two spaces 5 and 6. The partition wall 4 is L-shaped in its vertical section; the horizontal leg which lies on the floor 8 and is fixed thereto is denoted with 7. Close to the floor three horizontal .bores 9 are provided which are connected to vertical bores 10 so that the 'metal, whose flowing direction is illustrated by arrows, under formation of three flowing streams 11, is supplied in vertical direction to the surface of the metal sump in the tundish, whereby three waves or bulges 12 are formed. The distance a between the metal bath surface 13 and the upper margin 14 of the vertical bore may amount from to 3 to 30 cm; when the distance is too small owing to operational variations in the metal bath surface 13- the metal may sink under the upper margin 14 and then the metal may be oxidized; when the distance is too great there is the danger that not all non-metallic particles, which are illustrated in dots, get to the surface. Once they get to the surface and into contact with the slag layer 15, the non-metallic inclusions are immediately absorbed therein and kept there. The slag layer also protects the metal layer from oxidation and prevents an excessive heat dissipation by radiation. The height of the metal sump in the space 6, the outflow part of the tundish, is denoted with h,; preferably it amounts to from about 25 to 35 cm, and the thickness h of the horizontal part 7 of the separating wall 4 amounts to about cm. In the space 5, the inflow part, the height h of the metal is somewhat greater, i.e., the metal bath level 16 in the inflow part is somewhat higher than that in the outflow part. During casting in the tundish the inflow amount per time unit from the ladle l is equal to the outflow amount per time unit through the casting tube 18 into the mould 19. Thus, the throughflow amount per time unit must also be equal in the canals 9 and 10.

The speed v with which the metal stream flows out of the canals 9 and 10 is decided by the casting output or the throughflow amount per time unit and the canal cross section, the product of canal cross section and metal stream speed v corresponds to the casting output.

- At a given casting output the metal stream speed thus may be adjusted by an adequate dimensioning of the canal cross section. A specific adjustment of the metal stream speed is necessary in order to obtain the inclusion separating effect. It has to be adjusted in consideration of the distance a. In the following the relationship between a and v will be explained in greater detail.

Numeral l7 denotes the plane laid through the upper margin of the floor 8. The casting tube 18 which in known manner may be closeable by means of a (not shown) liftable and lowerable stopper is inserted into the opening of a water-cooled continuous casting mould 19, from which the cast bar 20 having a still liquid core 21 and a solidified bar shell 2 is continuously drawn out. Numeral 23 denotes supporting and guiding rolls. The casting level is suitably covered by a layer of casting powder 24 as a protection against oxidation and heat dissipation. When casting is ended the steel remaining in the inflow, part of the tundish may be drained by opening a tapping hole 25.

FIG. 2 illustrates 'the formation of three metal streams ll issuing from the bores 9 and I0, respectively, and forming waves or bulges 12 without rupturing the slag layer 15.

According to FIG. 3a separating wall 26 having a throughflow opening 27 close tothe floor 8 is provided. Behind the separating wall 26 the floor 8 is provided with a step 28, whose vertical part together with the separating wall 26 forms a vertical canal 29 from which a metal stream 30'flows upwardly towards the slag layer 15 giving off the non-metallic inclusions contained therein, under formation of a bulge 31.

6. In the diagram according to FIG. 4 on the abscissa the distance a is shown in cm and, on the ordinate the speed v of the metal stream flowing freely in upward direction from the bores 10 or the canal 29 is shown in cm/sec. Within the area of 3 to 30 cm found to be suitable for the distance a, the appropriate speed v is to'lie in the hatched field A; the speed thus may amount to from 3.5 to 17.5 cm/sec, when a has the smallest value, and increase proportionally up to maximally 31.0 to 45 cm/sec. when a has the greatest value. When, the lower marginal line 36 is not reached, the separation is insufficient (field C), when the upper margin 37 is trans gressed, owing to too high speed and occurrence of turbulent currents at the metal sump surface, the slag particles are drawn along, which, equally, makes for an insufficient separation (field B). Minor variations of a and v may occur during casting; this, however, is of no disadvantage when a and v are kept in the field A of FIG. 4 which in normal casting operation is easily possible. Numerals 32, 33 and 34, 35 are values for a which were obtained in the examples below.

In FIG. 5 numeral 1 denotes the lower part of a casting ladle from which a metal stream 2 flowsinto the tundish 3. Numeral 38 denotes a refractory tube which is open on both sides and provided with a lateral shoulder 39 with canals 40, 41 directed upwardly and which are connected with throughflow openings 42, 43 arranged close to the floor (FIG. 6). The tube 38 with its shoulder 39 rests on the floor 8 of the tundish 3; if desired, a refractory mass may be inserted between the contact areas, in order to seal the inner area of the tube against the tundish. The tube 38 has an about square cross section which is greater than that of the metal stream 2. The tube 38 penetrates the metal sump in the tundish. Numeral 44 denotes a refractory cover that may be set upon the tundish 3; the cover has an opening 45 through which the metal stream 2 may enter. This cover 44 lies on the upper margin of the tube 38 and presses the tube together with the shoulder 39 firmly against the floor 8 with its own weight, which isgreater than the buoyancy lift of the tube 38 generated bythe metal sump. Thus a releasable connection between the tube 38 and the shoulder 39 on the one hand and the floor 8 on the other hand is formed; the tube 38 may be removed without any difficulties after casting is terminated, so that the steel enclosed in the tube can be guided to the continuous casting mould; in-this operation method no liquid metal remains in the tundish 3. Since the tube 38 encloses themetal stream 2 during casting, an erosion of the side walls or of the front wall of the tundish 3 is avoided. Owing to the relatively small cross section and the small wall thickness of the tube 38 no great temperature losses occur while the metal flows through. The arrows denoted with numeral 11 indicate the current issuing from the canal 40, which current produces on the metal sump surface a wave or bulge 12 without rupturing the slag layer 15. The slag layer 15 receives the non-metallic inclusions of the liquid metal as soon as they get to the surface. After the metal is deflected, it flows through a casting tube 18 into a water-cooled continuous casting mould 19, from which a bar 20 with liquid core 21 and solidifled bar shell 2 is drawn downwardly and is cooled further until it is completely solidified. Numeral 23 denotes supporting and guiding rollers. The metal level in the continuous casting mould 19 is covered by a layer 24 of casting powder. Numeral 46 is a liftable and lowerable stopper for closing the casting tube 18 or for regulating the metal supply into the continuous casting mould l9.

In FIGS. 7 and 8 another embodiment of the tubular hollow body is shown, which is provided with a circular cross section; the shoulder 48, which is integrally connected with the tube 47 is provided with a single canal 49 directed in upward direction and connected with a corresponding opening 50 in the lateral wall of the tube 47.

In FIG. 9 numeral 51 denotes a tundish having a form similar to a inverted U; at the ends of the legs 52, 53 casting tubes 54, 55 are arranged each of which leads to one continuous casting mould. The hollow body 56 for deflecting the liquid metal is present in the middle part. As illustrated in detail in FIGS. 10 and 11 it comprises the tubular part 57 with an about square cross section and two opposed pedestal-shaped shoulders 58, 59 each of which is provided with canals 60, 61 and 62, 63, respectively, which are directed in upward direction and connected with corresponding openings 64, 65 and 66, 67, respectively, in the lateral wall of the tube 57. Thus, when metal flows into the tube 57, thetotal steel amount may be deflected upwardly and into the direction of the arrows in FIG. 9 via the casting tubes 54, 55 to two continuous casting plants.

Obviously the tubular hollow body may also be provided with other cross sections, and also other shoulders with canals that are directed upwardly may be present. The tube shaped hollow body with its shoulders is preferably formed in one piece of refractory ramming mass, in particular of mass containing a high degree of alumina, and burnt.

The process according to the invention is illustrated by the following examples:

I Example I On a continuous casting plant for steel slabs a steel comprising balance iron was cast. and a tundish according to FIG. 1 was used. The mould cross section amounted to 1,300 X 225 mm andthe lowering speed of the bar amounted to 0.73 vm/min; this makes for a casting output of 1.5 MT/min. v was fixed with about 13 cm/sec. from which a total cross section for the bores 9, of about 275cm was calculated; thus. each of the three bores 9 and 10 distributed uniformly over the cross section of the tundish had a cross section of 10.8 cm. b amounted to cm. In the flowing off part the metal sump was adjusted to aheight 'h, of to 28 cm so that a amounted to from 5 m8 cm. The means width of the tundish 6 amounted to about 75 cm and a mean cross section of the steel in front of or behind the separating wall 4 was calculated LII the wastes owing to metallurgically caused surface flaws. The sheets were cold rolled.

Example 2 On the same continuous casting plant a steel comprising:

C Si

balance iron was cast; whereby a tundish according to FIG. 1 was used, which, instead of three circular bores 9, 10, had a single rectangular canal for deflecting the steel and accelerating its flowing speed. The mould cross section amounted'to 1,000 X 225 mm and the lowering speed of the bar amounted to 0.75 m/min; this resulting in a casting output of 1.18 MT/min. For this example v was adjusted to about 22 cm/sec which corresponds to a cross section of about 128 cm h amounted to 15 cm. In the flowing out part the metal sump was adjusted to a height h, of 28 to 31 cm, so that a amounted to from 13 to 16 cm. As seen in direction of flow, the cross section of the steel in the tundish in front of or behind the separating wall amounted to from 2,100 to 2,330 cm in these areas thus the current speed of the steel is about 16 to 18 times smaller than in the rectangular canal cross section of about 128 cm Also under these conditions the separation of the aluminum oxides from the steel was satisfactory. At a loss due to flaming of only 0.5 percent by weight the waste amounted only to 0.7 percent of sheets produced from these slabs owing to metallurgical surface flaws.

As shown by these examples it is very simple to carry out the process according ,to the invention: prior to casting, a specific distance a (see FIG. 4) and an appropriate steel stream speed v is selected which are to be maintained during casting. In order to reach v during casting, with the help of the casting output the necessary canal cross section of the separating wall is calculated and a corresponding partition wall is inserted into the tundish. During casting then it is only necessary to adjust the casting level in the tundish to the chosen distance a.

We claim:

1. A process for separating non-metallic inclusions from hot liquidmetal in a tundish which is separated into first and second compartments, the second com partment containing a liquid metal sump covered by a slag layer, comprising:

supplying the metal to the first compartment; guiding the metal in the first compartment into the second compartment in the form of .at least one stream of metal, said stream originating at a preselected distance of from 3 to 30 cm below the metal sump surface and being directed at a speed in a certain range in anupward direction to impinge against the slag layer and form a wave therein, the speed of said stream being adjusted to remain within a range of from 3.5 to 31 cm/sec when the preselected distance is 3 cm and linearly increasing with distance to a range of from 1 7.5 to 45 cm/sec 3. The process set forth in claim 13, wherein the at least one stream is directed towards the surface of the metal sump covered by a slag layer at an angle of from 30 to 90.

4. A process for separating non-metallic inclusions from hot liquid steel comprising to 0.20 percent C, 0.25 to 1.60 percent Mn, 0.02 to 0.1 percent Al and O to 30 percent Si, balance iron, in a tundish of a continuous casting plant, said tundish being separated into first and second compartments and containing a liquid metal sump covered by a slag layer in the second compartment, comprising the steps of:

supplying the steel containing the impurities to the first compartment of the tundish; guiding the metal in the first compartment of the tundish into the second compartment of the tundish in the form of at least one stream of metal, said stream originating at a preselected distance of from 3 to 30 cm below the metal sump surface in the second compartment and being directed at a speed in a certain range in an upward direction to impinge against the slag and form a wave therein, the speed of said stream being adjusted to remain within a range of from 3.5 to 3] cm/sec when the preselected distance is 3 cm and linearly increasing with distance to range of from 17.5 to 45 cm/sec when the preselected distance is 30 cm; and

permitting the steel to flow out of the second compartment of said tu-ndish through at least one drain tube into a water-cooled mould from which a solidifying cast bar is continuously drawn out.

fig? i {,fU'NI En STATES PATENT OFFICE, ,j CERTI FICATE OF (IORRECTION j Patignt No, 7 3,311,1 7 Dated June 4, 1-974 luvehto rkt) a1 that err or appears in the above-identified patent and thgt salfi lgttets Patent are hereby csrtectedas shown below:

First page", ltem USI "Stahlwerke Alpine" should be I v --Stahlwerke Alpine--;

Firthpag, ItemJ-BO] "Nov. 14, 1971" should be '-N.ov. 4, t 1971"; "c0116,'11115 64,?*ish u '2" should be -shell 22--; Col; 7-, line 561, "means width" should read --mean width--; Cal. "8," 1ine ""65,""c1aim 13" should read ---claim l--; and

Col. 9," line 1, "claim 13" should read --claim l--.

Signed and sealed this 22nd day of October 1974.

,r l At-test: I

7 l V i Md ?G S c. MARSHALLDANN Attesting Officer Commissioner of Patents 

1. A process for separating non-metallic inclusions from hot liquid metal in a tundish which is separated into first and second compartments, the second compartment containing a liquid metal sump covered by a slag layer, comprising: supplying the metal to the first compartment; guiding the metal in the first compartment into the second compartment in the form of at least one stream of metal, said stream originating at a preselected distance of from 3 to 30 cm below the metal sump surface and being directed at a speed in a certain range in an upward direction to impinge against the slag layer and form a wave therein, the speed of said stream being adjusted to remain within a range of from 3.5 to 31 cm/sec when the preselected distance is 3 cm and linearly increasing with distance to a range of from 17.5 to 45 cm/sec when the preselected distance is 30 cm; and allowing the metal in the second compartment to exit through a drain in the second compartment.
 2. The process set forth in claim 13, wherein non-metallic inclusions are separated from aluminum killed soft steel.
 3. The process set forth in claim 13, wherein the at least one stream is directed towards the surface of the metal sump covered by a slag layer at an angle of from 30* to 90*.
 4. A process for separating non-metallic inclusions from hot liquid steel comprising 0 to 0.20 percent C, 0.25 to 1.60 percent Mn, 0.02 to 0.1 percent Al and 0 to 30 percent Si, balance iron, in a tundish of a continuous casting plant, said tundish being separated into first and second compartments and containing a liquid metal sump covered by a slag layer in the second compartment, comprising the steps of: supplying the steel containing the impurities to the first compartment of the tundish; guiding the metal in the first compartment of the tundish into the second compartment of the tundish in the form of at least one stream of metal, said stream originating at a preselected distance of from 3 to 30 cm below the metal sump surface in the second compartment and being directed at a speed in a certain range in an upward direction to impinge against the slag and form a wave therein, the speed of said stream being adjusted to remain within a range of from 3.5 to 31 cm/sec when the preselected distance is 3 cm and linearly increasing with distance to range of from 17.5 to 45 cm/sec when the preselected distance is 30 cm; and permitting the steel to flow out of the second compartment of said tundish through at least one drain tube into a water-cooled mould from which a solidifying cast bar is continuously drawn out. 